1. Field of the Invention
The invention relates generally to phase-stable manifolds and, in particular, a resonant waveguide for monitoring a scanning beam antenna essentially independent of temperature and frequency over a practical range and for monitoring a scanning beam antenna at a scan angle which is not aligned with the boresight direction of the antenna.
2. Description of the Prior Art
Slotted waveguides are sometimes used as aperture manifolds which couple to the radiated signal of a phased-array antenna to monitor its performance. Such waveguide manifolds are used in Microwave Landing System (MLS) ground systems for producing a signal equivalent to a signal viewed by a receiver at a specific angle within the coverage volume of the ground system. Ideally, such waveguide manifolds provide a far-field view of the scanning beam of the ground system and, additionally, measure the antenna insertion phase and amplitude associated with each individual array element.
Waveguide manifolds used to monitor elevation and azimuth scanning beams of an MLS ground system have been waveguides which propagate travelling waves and, consequently, the phasing characteristics are frequency and temperature dependent. The result is that the scan angle of the beam monitored at the waveguide output is also temperature and frequency dependent.